1. Field of the Invention
This invention relates to the preparation of biological smears on substrates for microscopic examinations.
2. Prior Art
Heretofore, smears of biological substances such as blood or cellular suspensions have been prepared for microscopic examinations by manipulation of microscope slides and slide cover slips. The technique requires a certain degree of expertise and, even with such skill, resulting smears have tended to lack uniformity and reproducibility. In the common manual preparation technique in which an end edge of an elongated slide is drawn lengthwise along a glass strip or another such slide to smear a droplet of blood on the last-mentioned slide, the heavier cellular material tends very strongly to move out or away from the central portion of the smear to be left on the smear in congregations along the margins thereof. This is undesirable for microscopic examinations. For such examinations it is desirable in many instances that the cellular distribution be substantially even across the width of the smear throughout any given portion of the smear.
It has been proposed that smears be prepared by a spinning process, an apparatus for carrying out such process has been commercially available. The process is one of centrifuging on a microscope slide a volume of biological fluid such as blood for a period sufficient to spread the specimen over a portion of the slide. A drawback in such use of spinners is that an excess of liquid specimen such as blood is spun off the slide to spray the environment such as ambient air and also splatter the inner wall surface of the spinner. Such blood specimens may carry infectious diseases, and hence the required cleanup operation of such spinners after use may be hazardous.
It is desired to obviate the aforementioned problems in the preparation of smears of biological substances. Moreover, it is desired to provide a method and apparatus for preparation of such smears which may be readily automated.